Powerful sound impulse generation methods and apparatus



April 23,V 1968 s. v. CHELMINSKI POWERFUL SOUND IMPULSE GENERATION S ANDAPFARATUS METHOD Filed NOV. 12. 1963 'Yeso @ack/ April 23, 1968 s. v.cHELM|NsK| 3,379,273

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POWERFUL SOUND IMPULSE GENERATlON METHODS AND APPARATUS Filed Nov. l2.1963 yl2 Sheets-Sheet '7 April 23, 1968 s. v. cHELMxNsKI 3,379,273

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POWERFUL SOUND IMPULSE GENERATION METHODS AND APPARATUS Filed NOV. 12.1963 l2 SheetS-Shee1l ll INVENTOR.

A /5/ BY y by MIM ,4 fran/frs April 23, 1968 S. v. CHELMINSKI POWERFULSOUND IMPULSE GENERATlON METHODS AND APPARATUS l2 Sheets-Sheet l 2 FiledNOV. 12, 1963 dhffe 2 2 @QN www1 u United States Patent O 3,379,273POWERFUL SOUND IMPULSE GENERATIN METHODS AND APPARATUS Stephen V.Chelminsiri, Redding, Conn., assigner to Bolt Associates, inc., EastNorwalk, Conn. Continuation-in-part of application Ser. No. 151,853,Nov. 13, 1961. This application Nov. 12, 1963, Ser. No. 322,677

28 Claims. (Cl. 181-5) ABSTRACT 0F THE DISCLOSURE Methods and systemsgenerating and utilizing powerful acoustical waves produced underwater,useful for reection or refraction types of seismic surveys or for combilnations of these. Compressed air fed to acoustical impulse generatorapparatus is confined therein, electrical signals produced for firing tosuddenly release the confined compressed air generating powerfulacoustical waves. The

pressure of compressed air is applied for re-closing the d Thisapplication is a continuation-in-part of my prior -copending appiicationSer. No. 151,853, tiled on Nov. 13, 1961, which issued on May 3, 1966,as Patent No. 3,249,177.

The present invention relates to powerful sound irnpulse generationmethods and apparatus and relates to the art of sound instrumentation,and particularly to a new and improved pneumatic acoustical repeater andto methods and apparatus utilizing the impulses including seismicexploration systems utilizing powerful sound impulses generatedunderwater.

Among the many advantages of the sound impulse generation methods andapparatus which are described herein as illustrative of the presentinvention are those resulting from the fact that an abrupt and clear-cutsound impulse is produced and is readiiy repeatable as desired. Thesepowerful sound impulses are useful for many purposes, for example, asharply-defined powerful boom is produced underwater and having a highintensity 'and penetrating ability for seismic exploration. Moreover,the sound impulse generation methods and apparatus of the presentinvention enable the use of compressed air for generating a powerfulsound impulse underwater and enable the powerful sound impulse to berepeated conveniently at frequent and accurately timed intervals, forexample, such as once every two seconds and in many cases atshorterintervals if desired, from a single acoustical impulse generator, alsoreferred to herein as an acoustical repeater. In addition, this soundimpulse generator can be operated for long periods of time, for example,for a day, while continuously producing powerful sound impulses at thesefrequent intervals. The compressed air is utilized to advantage inetfectuating its own sudden release in response to an electric triggersignal.

The methods and apparatus of the present invention enable seismicexploration surveys to be made of the conditions and characteristics ofthe bottom and sub-bottom formations beneath bodies of water and ofobjects in the 3,379,273 Patented Apr. 23, 1968 water land of shorelineconditions and characteristics either from or to a moving vessel or fromor to a stationary vessel, including aircraft and lighter-than-aircraft. Also, the powerful sound impulses enable either reection orrefraction types of seismic surveys to be made and also combinations ofthese types of surveys. These powerful sound impulses are adapted fortransmission over long distances horizontally through the water as wellvertically and are adapted to be conducted long distances in one or moregeological formations or strata and to emerge at one or various pointsdistant from the place of entry, thus providing information aboutcharacteristics of the stratum or strata involved. There is an initialperiod of time during which the compressed gas is retained undersubstantially full pressure and then an abrupt transition to the fullrelease of this air so as to create an abrupt and clear-cut powerfulsound impulse.

Among the further advantages of the powerful sound impulse generationmethods and apparatus described herein are those resulting from the factthat the seismic sound generator unit, acoustical repeater, as describedis adapted to build up and store energy in the form of compressed airwithin the unit underwater. A powerful sound impulse is generated bysuddenly and abruptly releasing this compressed air directly into thewater as desired, thus creating a strong sharply-defined acoustic wavehaving high penetrating ability. A relatively high eiciency of acousticwave generation is provided by virtue of the fact that the compressedair acts directly upon the surrounding -body of water, as compared withthe eiciency of exploding gas systems which explode gas from ambientpressure or the eiciency of the electrical type of systems wherein theelectrical energy is converted to heat energy and/or to chemical energyto expand and/or to dissociate or electrolyse the water or is convertedto electromagnetic forces which in turn are used to move masses for thegeneration of sound.

While the methods and apparatus of the invention are applicable for manypurposes as will be set forth further below, they are illustrativelydisclosed and described as applied to underwater sound instrumentationsuch as oceanographic equipment and systems that are employed in seismicexploration of the worlds crust under and adjacent to bodies of water.

Since water is such a good sound conductor, it is unnecessary togenerate sound waves right on or in the ocean oor; they can be producedin the water near the surface, The pressure waves travel down throughthe water to the ocean floor and are reflected as in the usualecho-sounding techniques. However, these waves also penetrate into theocean fioor and are reflected from the substrata. These acoustic wavespropagate horizontally through one or more geological strata and may berecorded at a distance from the source, thus providing useful refractiondata on the stratum or strata involved.

While explosives for marine seismic work can put large amounts of energyinto the water and obtain great depth of penetration, they do havedrawbacks; they are dangerous to handle and use, and in some areas suchas congested harbors, they cannot be used at all. Also, each shot costsmoney which can run into many thousands of dollars per survey.Explosives tend generally to concentrate substantial amounts of theirenergy output into higher frequency components which may not bedesirable for many purposes; whereas, the sound impulse generationmethods and apparatus of the present invention can be adjusted over alarge amplitude range and adjusted in frequency so as to provide thedesired spectrum distribution of sound frequencies for the purposes athand. The methods and apparatus of the present invention provide a greatexibilty in operation; the sound intensity and characteristics can beconveniently adjusted by adjusting the pressures and volumes ofcompressed air being released.

The present invention is illustratively described as embodied in adevice capable of emitting a large amount of acoustical energy intowater in the form of a clear, repeatable pulse, the frequency andamplitude of which may be readily varied. These powerful sound impulsesare well adapted for use in seismic exploration systems and also can beused to advantage for other purposes.

It is an object of the present invention to improve the methods andapparatus for powerful underwater sound impulse generation.

A further object of the present invention is to provide improved seismicexploration and survey systems.

Another object of the present invention is to improve the art of seismicexploration and surveying of the earth beneath bodies of water and theseismic exploration and surveying of the earth near bodies of water.

A further object of the present invention is to improve the methods andapparatus for the convenient sudden re- L lease of gases underwater orin other fluid media for the generation of strong, well-defined acousticwaves and pressure waves for a wide variety of useful applications asdescribed further below.

Among the many objects of the present invention is` l to provide anacoustical repeater by which a large amount of sound energy can beproduced with a relatively small device, and to provide a pneumaticacoustical repeater which is convenient and safe to use for a widevariety of functions and purposes and providing a power source for utools and machines to shape and form materials and objects, to punch andshear materials and objects, and to loosen, heave and dislodge mineraldeposits. As used herein the term acoustical repeater is intended toinclude acoustical impulse generator repeaters which may be operatedwith gases supplied thereto or under high pressure or generated thereinunder high pressure and including -compressed air as well as other gasesas may be desirable in various applications. In most instancescompressed air is used, but it is to be understood that the termacoustical repeater is not intended to be limited to air-operatedapparatus, as will be pointed out in the detailed description furtherbelow.

The various objects, aspects and advantages of the present inventionwill be in part more fully pointed out and in part will be understoodfrom a consideration of the following specification in conjunction withthe accompanying drawings, in which:

FIGURE 1 is an illustration of a seismic exploration system' utilizingpowerful sound impulse generated by the sudden release of compressed gasunder water in response to electrical control signals and embodying thepresent invention;

FIGURE 2 shows in detail the acoustical impulse generation system ofFIGURE l and includes a sectional view of an acoustical repeater andschematic diagram of associated fluid conducting and electrical controlcircuits as used in the system of FIGURE l;

FIGURES 3 and 4 show modified acoustical impulse generation systemsadapted for use in seismic exploration systems similar to that shown inFIGURE 1;

FIGURE 5 is an elevational sectional view of an acoustical repeaterwhich may be used in these systems;

FIGURE 5A is a partial sectional view showing a modification of theapparatus of FIGURE 5;

FIGURE 6 is a cross sectional view of the pneumatic acoustical repeaterof FIGURE 5 taken along the line 6 6 of FIGURE 5;

FIGURES 7, 7A and 7B are elevational views showing vent openings ofdifferent configurations;

FIGURE 8 is a sectional view taken along the line 8 8 of FIGURE 5looking down;

FIGURE 9 is an axial sectional view of seismic sound impulse generatorrepeater apparatus adapted t `be llSed d in surveying and explorationsystems such as those shown in FIGURES 1-4;

FIGURE 10 is a cross section of FIGURE 9 taken along the line 1li-1f) inFIGURE 9 and looking back;

FIGURE 1l illustrates a modified pneumatic acoustical repeater which maybe used in the foregoing systems;

FIGURE 12 is a cross section of FIGURE 11 taken along line 12-12 ofFIGURE 11; and

FIGURES 13 through 20 inclusive Show further modified acousticalrepeater apparatus which may be used in the foregoing systems. FIGURE15A is a partial sectional view showing a modification of the apparatusof FIGURE 15. The apparatus shown in FIGURES 14 and 17 are adapted tohave fuel injected therein; the apparatus shown in FIGURES 18 and 19 areadapted to have their effective volume controlled and adjusted remotelywhile the apparatus are submerged in use; and FIGURE 17A is anothermodification adapted to have fuel injected therein.

When carrying out a seismic survey exploration utilizing the methods andapparatus of the present invention, for example as shown in FIGURES 1and 2, a survey ship 20 proceeds along a known course 21 on a body ofwater 22, for example such as an ocean, sea, lake, river, or sound, andthe ship 20 tows seismic sound impulse generator repeater apparatus 23and hydrophone equipment 24. This hydrophone equipment 24, is of knowntype, for example and may include a single device responsive toacoustical energy in the water 22 or may include a predetermined patternof such devices, for example such as a line of hydrophones strung outbehind the ship at uniformly spaced intervals. The particulararrangement, pattern or array of hydrophone devices depends upon theparticular type of seismic survey being performed, as is known in theart and the methods and apparatus of the present invention provideadvantages in performing a wide variety of types of such surveys.

The hydrophone equipment 24 is connected through electric cable means 26extending to the ship, and on board the ship is suitable recordingapparatus, which is generally indicated at 27 (FIGURE 1) and is shown ina Schematic illustration. This recording apparatus 27 may be of anysuitable known type, for example in the illustrative survey system shownin FIGURE l, the apparatus 27 includes an amplifier 28 having inputconnections 29 from the hydrophone cable 26. This amplifier 28 is ofknown type, for example such as is available commercially, and hasoutput connections 30 and 3'1 extending to an electrical contact bar 32and to a platen roll 33, respectively, in chart recording apparatus 34.This graphic recording apparatus 34 may be of any suitable known type,for example such as is available commercially from Westrex Co. Divisionof Litton Industries, New York, N.Y.

During operation a recording paper chart 35 is suitably driven past theplaten roll 33, as indicated by the arrow 36, and one or more recordingstyli 37, which are attached to a driving belt, are sequentiallytraversed laterally across the front surface of the chart 35 in theregion `where the rear surface of the chart is engaging the platen 33.The driving belt 38 travels around a pair of pulley wheels 39 and 40 soas to scan each stylus rapidly across the face of the chart. Each stylusincludes an electrical brush element 41 which remains in contact withthe bar 32 as the stylus scans across the chart. Consequently, theamplified electrical signals from the amplifier 28 are recorded on thechart 35.

For driving the recording stylus mechanism an electric motor 42 has amechanical drive connection 43 to a drive wheel 44 which is mechanicallyconnected so as to drive the pulley ywheel 40.

In order to actuae the acoustical seismic impulse Igenerator repeaterapparatus 23 in repetitive cycles, for example, such as every twoseconds, main control means 45 (FIGURES 1 and 2) are provided on boardthe ship and are arranged to operate in predetermined synchronizedrelationship with respect to the scanning movement of each stylus 37.This control means 45 transmits control signals at cyclic intervals tothe impulse generator repeater apparatus for controlling its operation.Also, in this system the control apparatus 45 feeds a signal to therespective stylus 37 which is scanning the chart 35 s0 as to record amark 46 on the chart at the instant when a control signal is sent to theapparatus 23 for causing an acoustical impulse 47 to be emitted into thewater from the apparatus 23. The line of these initial marks 46 on thechart is identified as the fire line F and serves as a reference fromwhich to determine by measurement on the chart the characteristics ofthe earths crust adjacent to the body of water 22. It will beappreciated that other suitable arrangements may be made for providing areference line or mark on the chart for the purpose of providing a timebase or datum line from which the relationships of the other recordedsignals may be measured and analyzed, for example, the line D of marksmay be used as the datum line.

.Each acoustical impulse 47 is propagated through the water 22 so as totravel outwardly away from the sound impulse generator repeaterapparatus 23. These impulses are cyclically repeated at frequent,accurate timed intervals, for example, such as once every one or twoseconds. A portion of each impulse travels along a direct path D to thehydrophone equipment 2'4 and produces the line D of marks on the chart35. At a later interval of time the portion of each acoustical impulselwhich was reflected from the top of a sediment layer beneath the water22 reaches the hydrophone equipment 24 along the rst reflection path R1so as to produce a line of marks R1 on the chart. Then subsequently, theportion of each acoustical impulse which was reflected from theinterface between the sediment layer and bedrock reaches the hydrophoneequipment 23 alon-g a second reliection path R2 so as to produce a lineof marks R2 on the chart. Thus, the plots of the received acousticalsignals produce an advantageous record of the characteristics of theformations beneath the body of water. When additional interfaces arepresent, such as a deposit of glacial material, then additionalreflection paths are present so as to produce additional plots, such asthe line of marks R3 on the chart.

In this illustrative system, more particularly illustrated in FIGURE 2,the main contr-ol means includes one or more signal controlling means48, 49 and '50 which are cyclically operated in synchronizedrelationship with the chart recording apparatus 34. For example, thesignal controlling means 48, 49 and 50 are illustratively shown inFIGURE 2 as being switch controlling cams which are mechanicallyinterconnected as indicated at 51 so that all of these cams 48, 49 andare revolved in synchronized relationship with each other and with thestylus scanning movement. A positive drive connection 52 (FIGURE 1),such as by timing belt, is provided between the drive wheel 44 and thecams 43, 49 and 50.

In order to transmit the cyclic control signals for actuating theacoustical apparatus 23, switch means 58, 59 and 6i) (FIGURE 2) areoperated in sequence by the respective controlling means 4S, 49 and 50.The switch means 58, 59 and 60 are all normally open and they are closedwhen one end of their actuating levers 64 moves down into recessedregions of the respective cams so as to depress the switch buttons 65.The switch means 5S is connected by a pair of leads 55 and 56 withelectric cable means 57 (FIGURES l and 2) extending to the acousticalimpulse generator repeater apparatus 23. In this system the lead 55 is acommon connection, as shown in FIGURE 2, and the wire line 56 extendsthrough the cable 57 to electrically opera-ble liring means 61 forcontrolling the impulse generator apparatus 23, as will be explained indetail further below. Similarly, the second switch means 59 has oneterminal connected to the common line 55 and the other terminal isconnected through a wire 67 extending through the cable 57 toelectrically operable return means 62 for controlling the impulsegenerator apparatus 23, as explained further below. The third switchmeans 60 has one terminal connected to the common lines 55 and its otherterminal connected by a wire 68 extending through the cable 57 toelectrically operable till means 63 having a control function explainedfurther below. The commonline 55 is connected to one terminal of anelectrical power source 69, for example a battery or generator source onthe boat 20. The other terminal of this electrical source 69 isconnected -by a common line 66 extending through the cable 57 to thefire, return, and lill control means 61, v62 and 63, shown as threenormally closed solenoid valves which are opened respectively, when theyare energized from the source 69.

For providing the reference line F of the marks 46, the switch means 58includes a second set of normally open contacts connected to a source ofpotential 53 and through a coupling network 54 to the input of theamplier 28. Consequently, upon the instant of closure of the switchmeans 58, there is a brief electrical pulse which is supplied to theamplilier 2S for creating the reference l-ine F. It is noted that theleading edge 71 of the recessed sector A is sharply delined so that theswitch means 58 is snapped closed with a quick movement for providing aclearly defined and accurately timed beginning of each tiring cycle.

From the above description of the over-all control circuit it will beunderstood that during operation the lire control means 61 is energizedby the source 69 during the time period when the recessed sector A ofthe cam 48 passes beneath the end of the actuating lever 64 for theswitch means 58. Subsequently, the return control means 62 is energizedby the source 69 when the recessed sector B of the cam 49 passeslbeneath the end of the actuating lever 64 for the switch means 59. Asindicated in FIG- URE 2, there is an angular spacing between the sectorsA and B so that the return control means 62 is not operated until afterthe apparatus 23 has completed its tiring operation and has emitted thepowerful acoustical impulse 47. The completion of the cycle is made byenergization of the lill control means 63, which occurs when therecessed sector `C of the cam 50 passes beneath the end of the actuatinglever 64 of the switch means 60. The initial portion of the lill periodC overlaps the latter portion of the return period B so as to assurethat the apparatus 23 is held in its returned condition when the lillingoccurs. lt is noted that the length of time of the till period C is manytimes longer than the lire period. As will be explained in detailfurther below the actual tiring time of the apparatus 23, which includesan acoustical repeater 70, is very brief, being of the order of a fewmilliseconds for the sudden complete release of the high pressure gasfrom the apparatus 23.

In order to supply gas under high pressure to the impulse generatorrepeater apparatus 23, the system includes a suitable source 72 of highpressure gas located on the ship 20. In this system the gas being usedis compressed air, and the source 72 includes a prime mover drive motor73 running a multistage air compressor 74, which is capable of supplyingcompressed air at pressures up to and in excess of 2,000 pounds persquare inch. The output of the compressor 74 feeds through a moistureand oil separator 75 into a high-pressure storage tank 76. Thecompressed air is supplied from the tank through a shutoit" valve 77 andthrough a first lter 78 into a pressure regulator 79 having a manualadjusting control 80 which is set at a desired pressure level, forexample such as 2,000 p.s.i. At the output of the regulator is apressure gauge S1 and a pipe coupling 82 connected to a llexiblehigh-pressure fluid supply hose 83 extending to the impulse generatorrepeater apparatus 23. Included in the apparatus 23 is a second filter84 having a porous bronze filter element or similar lter rbarrierelement for pre- 7 venting the entry of dirt particles or bers into theapparatus 23.

Beyond the filter 84 the hose line branches and one branch 85 isconnected through the normally-closed return control valve 62 andthrough a hose line 86 to return means 37 in the acoustical repeater 70,as shown also in greater detail in FIGURE 5. The other branch 33 of thehigh-pressure fluid supply line 83 is connected through thenormally-closed fill control valve 63 and through a hose line 89 into atill port 91) entering the repeater '70. Aso, a tiring hose line 91branches from the line 89, and this firing line 91 provides afluid-conducting passage extending to a firing port 92. This tiringpassage 91 is normally shut off by the firing control valve 61.

Although a pair of control valves 61 and 63 are illustrated in FGURE 2for providing the filling and firing functions, it will be understoodthat they can be replaced by a single three-way connection solenoidvalve located at the junction of the lines 88, 39 and 91 for providingthese two functions, for example as shown in the system in FIGURE 11.

Referring particularly to FIGURES 2 and 5, the acoustical repeater 70 asillustratively shown comprises container means adapted to hold fluidtherein under high pressure and to discharge the fluid suddenly in avery brief time period in response to an external control signal.Because of the fact that the repeater 71'! is cyclieally subjected tohigh stresses in operation and is exposed to corrosive environmentalconditions, for example, it may be submerged in salt `water for longperiods of time, it is constructed of high-strength corrosion resistantmaterial, such as high strength stainless steel. The container means 94includes a plurality of axially aligned cylinders each having a pistonin sliding engagement therewith. These pistons are rigidlyinterconnected so that they are capable of movement with very greatacceleration over a predetermined distance before suddenly dischargingthe high-pressure fluid through vent means from the repeater '79'. Oneof these pistons serves as opening and closing means for containing andthen releasing the high pressure fluid. and another piston serves asoperating means for the first piston for holding it closed and then forreleasing it in response to the external firing signal so that thepistons then move with very great acceleration before the first pistonopens the vent means for discharging the highpressure fluid.

Consequently, the vent means are opened abruptly, for the first pistonis travelling very fast at the instant when the vent means are opened,thus advantageously providing an effectively instantaneous transitionfrom fully closed to fully open condition.

As shown illustratively in FTGURES 2 and 5, the container means 94includes a first cylinder 95 which extends toward vent means 96 and asecond cylinder 97 which is axially aligned with the first cylinder S35.A first piston 93 travels along the cylinder 95 and serves as closingmeans for blocking the discharge port so as to contain the high-pressurefluid within the container means 94.

For operating the first piston 98 there is a second piston 99 whichtravels along the cylinder 97, and these two pistons are rigidlyinterconected to form a shuttle 1th? which is constructed so as to be aslight as possible while being sulliciently strong to withstand a verygreat acceleration and subsequent very great deceleration in the axialdirection. A hollow piston rod 1tl1 rigidly interconnects these twopistons 98 and 99.

When the shuttle 160 is in its normal position prior to firing, thefirst piston 98 is located at the upper end of the cylinder 95 remotefrom the vent means 96. The rim of the piston 98 is in sealingengagement with a first annular resilient seal 102 which is clamped inplace by a metal clamping retainer ring 1113 held by an internalshoulder 164 at the lower end of the cylinder 97. The seal 102 is formedof a very tough, resilient material, for example, tough, solidpolyurethane, and it has sutlicient ability to be bent and yet to returnto its original shape so as to enable it to be slid over the perimeterof the piston 93 when the shuttle 190 and seal 1132 are being assembledand suilicient durability to withstand the operating conditions. Fromexperiments I have found that it is desirable to machine the two pistons93 and 99 and the hollow connecting rod 161 as an integral member so asto provide sufficient strength and durability to withstand the verygreat acceleration and deceleration forces and pressures encounteredduring operation repeatedly over thousands of operating cycles.

Y The cylinder includes a strong flange 166 mating with a strong flange107 on the lower end of the cylinder 97. The upper end of the cylinder95 projects somewhat above the top surface 1118 of the ange 156 so as toform a lip 1159 engaging with the lower end of the upper cylinder belowthe internal shoulder 1114 for precisely aligning the two cylinders. Theflange surface 168 has an annular groove containing an O-ring 111iabutting against the flange 107 preventing leakage of high pressurefluid from the housing 94. A bolt circle 112 holds the flanges and 1117tightly together.

In preparation for firing, gas under pressure, for eX- ample 2,000p.s.i. is introduced through the fill port 90 into the chamber 113within the cylinder 97. The pressure of the gas upon the upper surface K(FIGURE 5) of the piston 98 is tending to drive this piston down alongthe cylinder 95.

In order to hold this piston in place, the second piston 99 has asurface L (FGURE 5) exposed to the pressure fluid in the container andof larger effective area than area K and facing in the oppositedirection from area K. This second piston has an annular lip sealingelement 114 engaging up against a second annular tough resilient seal115. This seal 115 may be formed of the same material as the seal 102. Aclamping retainer ring 116 is held against the outer edge of the seal115 by an internal shoulder 117 at the upper end of the cylinder 97. Theinner edge of the seal 11S is held by a retainer disc stop 118 having arabbeted edge overlapping the seal 115. A plurality of bolts 119 securethe disc 118 against the cylinder head wall 124i. This end wall 120 isfastened by a bolt circle 121 to a flange 122 on the cylinder 97. Thewall 12) includes an annular groove containing an O-ring 123 forpreventing leakage of the high pressure fluid from the housing 94.

As will be explained, when the repeater 79 is fired, the pressure withinthe chamber 113 drops very abruptly. Consequently, it is desirable toprevent the accumulation of any high pressure fluid behind the seal 115,because any such pocket of gas would tend to blow the seal 115 away fromthe end wall 129 upon firing. Accordingly, a small diameter bleed hole124 passes through the end wall 12) and communicates with a bleedchannel 125 behind the seal 115. The outer diameter of the sealing lipelement 114 is greater than the diameter of the piston 98. The uppersurface M of the piston 99 engages against the -retainer and stop disc118 as the lip 114 begins to press into the resilient seal 115. Thisstop 118 prevents the large thrust of the piston from embedding the lipelement 114 deeply into the seal 115.

The shuttle 1G@ is in effect in unstable equilibrium, being temporarilyheld in place by the differential in areas, but as soon as the pressurenears equalization on opposite surfaces of the operating piston 98, thenthe shuttle is released and accelerates violently.

In order to fire the repeater 70, communication is provided between thechamber 113 and the upper surface M of the piston 99 so as to tend toequalize the pressures against opposite sides L and M of the operatingpiston 99. A passage is completed from the fill port 90 through the line91 to the firing port 92 by opening the tiring valve 61. There is asmall chamber 126 surrounding the firing port 92 adjacent to the surfaceM of the piston 99, and the high pressure fluid enters through the port92. into URE 8) in the scalloped periphery of the piston 99 so l0 as toequalize completely the pressure against opposite sides M and L of thepiston 99. As shown in FIGURE 8, the lands 128 between the by-passopenings 127 serve as guide means travelling 'along the cylinder surface97. It will be understood that these by-pass openings 127 may also beprovided by lan-ds 128 (FIGURE 5A) extending along the cylin-der Wall.

For imparting a slight rotation to the pistons 9S and 99, the by-passopenings 127 are skewed as shown in FIGURE 8 and the gas rushes throughthese openings to provide a torque reaction. Thus, advantageously thepistons 98 and 99 are turned in position between each tiring stroke soas lto avoid continued wear of the lands 12S always along the sameaxially extending lines on the cylinder surface 97.

The two pistons 9S yand 99 accelerate downwardly with very greatacceleration along the acceleration distance E, but the high pressuregas is prevented from escaping through the vent means 95 until after therim of the piston 93 has passed below the upper end of the vent means96. The vent means 96 (please see also FIGURE 6) comprise a plurality ofopenings to the exterior of the housing means 94 and communicating withthe lower end of the cylinder 95. The vent means 96 are in the lower endportion 130 of the housing means 94, and the longitudinally extendingareas 131 (FIGURE 6) between each of the vent openings serve as guidesurfaces for guiding the piston 98.

As the piston 93 travels -along the acceleration distance E, itaccelerates extremely rapidly to a high velocity so that the piston 98passes the end 132 of the cylinder 95 extremely fast and traverses pastthe vents 95 almost instantaneously so that they become fully open in aminute fraction of a second. To explain this advantageous high rate ofspeed of opening, the following discussion is believed to be helpful.

In this illustrative example the chamber 113 has a volume of one hundredthirty-tive cubic inches and is charged with compressed air to apressure of 2,000 p.s.i. The diameter of the opening piston 98 is 3.1inches, and the acceleration 4distance E is one inch. The shuttleaccelerates to la velocity in excess of 4() feet per second before theopening piston 98 begins to open the discharge openings 96. Thus, thecompressed air is all released within a few milliseconds after thepiston passes the end 132 of the cylinder 9S. The high pressure gas isthus released with effectively an extremely abrupt discharge whichapproaches explosive abruptness.

However, in addition to the many other advantages, this abrupt releaseof gas under water creates a seismic boom providing energy in the lowfrequency end of the acoustic spectrum, for example the repeater 70 canbe arranged to provide substantial sound energy below 100 cycles persecond. This intense low frequency acoustical impulse has lgreatpenetrating ability into the various layers and formations -of earth soas to provide a good legible chart record, including indications of verydeep formations. For example, in a deep body of water having 3,000 feetof depth a record may -be obtained of formations down to 3,500 feetbelow the bottom of the water, i.e., a total depth of 6,500 feet belowthe ship and often deeper. Advantageously, the acoustical impulse can berepeated hundreds or thousands of times at frequent accurately timedintervals, of the order of a few seconds, e.g., once every two seconds.Also, the repeater 70 can be arranged to provide substantial soundenergy at higher frequencies, for example above 1,000 c.p.s. which isdesirable for certain types of surveys such as ones in shallow water.

In distinction to this system it is noted that when explosives are used,such desirable repetition at frequent intervals and such contro-l overthe sound energy spectrum is not obtained and in many instances thesound energy released by the explosion does not have such desirablecharacteristics as the acoustical impulse generated by the methods andof the present invention.

In order to decelerate the pistons 93 and 99 quickly ybut smoothly nearthe end of the stroke, thel housing means 94 includes a stop surface 134which is in opposed relationship to the surface N of the piston 9d. Asthe -piston 9S nears the end of its stroke the water between theapproaching surface N and 134 is accelerated generally radiallyoutwardly, providing -a retarding force reaction against the surface N.Moreover, the converging lower ends of the vents 96 cooperate with therim of the piston 9S to form throttling means, i.e., flow control means,progressively restricting the egress of the water so as to increase thedeceleration rate until the piston is brought to rest adjacent to thesurface 134.

The repeater 79 shown in FIGURE 5A is similar to the repeater 70 ofFIGURE 5 except that the piston 99' has a circular perimeter, and theby-pass passages 127 comprise grooves extending along the cylinder wall97 with lands 123 between these grooves. The pressure iiuid rushesthrough these `by-pass passages 127 as indicated by the iiow arrow inFIGURE 5A as the shuttle accelerates very rapidly downwardly as shown bythe arrow, and the lands 128' serve `as guides for the piston.

As shown in FIGURES 7, 7A and 7B, various configurations of vents 96 maybe used to provide different etiective rates of discharge and of pistondeceleration. As explained above the configuration of FIGURE 7 provides`a very abrupt discharge of the high pressure fluid and a smoothdeceleration.

The rectangular vent configuration of FIGURE 7A produces a very abruptdischarge and an abrupt deceleration of the piston at the end of itsstroke. This rectangular configuration generally provides the maximumeffective vent area for a given stroke, which is of advantage forcompact repeater devices wherein the stroke is desired to be relativelyshort.

In the vent configuration of FIGURE 7B, the initial diverging end 132provides a modified discharge rate of the high pressure iiuid so as toreduce the initial portion of the discharge iiow below that occurringwhen using the configuration shown in FIGURES 7 and 7A.

After the conclusion of the firing, the pistons 9? and 99 are returnedto their initial positions by supplying fluid to the return means S7.The return means 87 cornprise a pedestal `137 having a bore 138 andincluding suitable sealing means 139 adjacent to its end, for examplesealing means such as piston rings, O-rings, and the like, iitting ingrooves on the pedestal. The iiuid is supplied through the line S5 andthrough the bore 138 into a cocking chamber 149 within the hollow pistonrod 101. In etl'ec't this iiuid cooperating with the return means 87acts as resilient means for returning the pistons 98 and 99 to theirinitial position. For rigidity the pedestal 137 includes a large baseflange 141 (FIGURE 5) engaging the end 13) of the housing means.

When it is desired to obtain the greatest possible acceleration of thetwo pistons, then the return iiuid is allowed to escape from the cookingchamber 149 after the return solenoid valve 62 is closed, so that thereis a minimum amount of iiuid in the chamber 14d which would somewhatimpede the downward acceleration of the pistons. This return iiuidbleeds out through a small passage 142 (FIGURE 5) and through a checkvalve in a tling 143 communicating with the cooking chamber so that thepressure in chamber 145i returns substantially 'l l to ambient. rlhischeck valve prevents the entry of water into the coclzing chamber 14'.

A bleed hole 114/3 (FGURE 5) communicating with the tiring port '$2prevents any accidental rise in pressure in the hiring chamber 126 andthus avc-ids any possibility for accidental seit-tiring of the repeater7), in the event it remains fully charged for long periods of time.Thus, any minute amount of high pressure tluid leaking past the sealingmeans 114, 11S over a long period of time is prevented from accumulatingin the tiring chamber 126.

In the remaining iigures ot' the drawings parts and elements performingfunctions corresponding to those f FIGURES 1, 2, and -7 havecorresponding reference numbers. The system of FIGURE 3 is identical tothat described above, except that the control means A includes onlytiring and rilling control means and correspondingly the impulsegenerator repeater apparatus includes only two solenoid valves 61 and 63and asiociated circuit connections. The return means S7 is continuouslysupplied during operation with return fluid provided by apressure-regulating valve 145 in the line 86. This valve 145 is set at apressure somewhat above the ambient pressure at the depth of operation.By virtue of the fact that this valve is on continuously and thepressure in the cooking chamber 140 is considerably below the highpressure of the rain charge, the bleed passage 142 (FlGURE 5) and checkvalve 143 may be omitted from the repeater 79A used in the system ofFIGURE 3. Although a pair of control valves 61 and 63 are illustrated inFIGURE 3, it will be understood that they can be replaced by a singlethree-way connection solenoid valve located at the junction of the lines88, 89 and 91 for providingy the tilting and tiring functions as shownin the syste-m ot FIGURE 11.

In summary it is noted that the chamber 113 in the repeaters 76, and 79Awithin the cylindrical surface 97 serves as a combined operating andcharge-containing chamber, as shown in FIGURES 2, 3, 5 and 5A.

The system illustrated in FIGURE A. is generally similar to the systemsof FIGURES 1-3 and 5-7, except that the repeater 70B, as shown ingreater detail in FIC- URES 15 and 16, includes a combined `coclting andoperating chamber 14S dened by the cylinder 97 in addition to acharge-containing chamber 113 within a cylinder 15@ of the housing 94and a cylinder 9S along which the piston g3 is accelerated through adistance E (FIGURE 15). This repeater 7GB includes a middle portion 151having vent means 96 (FlGURE 16) at the lower end of the cylinder 95.The middle portion 151 has an annular guide 152 slidingly engaging thehollow piston rod 1G31, and a piston ring 149 surrounds this rod.

In operation during the rcturn-and-ll part of the cycle thehigh-pressure iuid is introduced into the chamber 148 and serves toreturn the shuttle 169B so as to seat the sealing element 114 up againstthe resilient static seal 11S. The uid passes up through a passage 153in the piston rod 1F11 and into the charge-containing chamber 113 totill it also. A construction 154 (FIGURE l5) in the passage 153maintains the pressure in the chamber 14S above that in the chamber 113during the beginning of the return and till sequence so that there isprovided a net upward thrust on the projected area of the piston rod 161exposed to the pressure of the uid in the chamber 148, said pressurebeing retained by the piston ring 149. This net upward thrust assuresthat the sealing lip element 114- remains seated firmly during theinitial portion Of the ll cycle as the uid begins to be introduced. Theeffective area L of the operating piston 99 exceeds the effective area Kof the closing and opening piston 98 and holds this piston in its closedposition as the iilling continues.

After the chamber 113 is filled up to the desired pressure, then theapparatus 23B (FIGURE 4) is tired at the appropriate instant by openingthe ring solenoid valve o1 so as to provide communication between thehigh-pressure 'Fluid and the top surface M (FIGURE 15) of the piston9E?. This tlow tends to equalize the pressure against Opposite surfacesL and M of the operating piston 99. As soon as the sealing element 11d'Ihas left the seat 115, then the iiuid rushes up through the openings 127in the scalloped perimeter of the piston 93. These openings 127 areinclined to provide a torque reaction for rotating the shuttle 109B.

The pistons 98 and 99 pick up speed with very great acceleration as thepiston 98 travels through the acceleration distance E, and thus thepiston SiS is moving at a high rate of speed as it passes the end 132 ofthe cy.inder so as to open the vents 96 very abruptly.

There is a conical stop surface 134 (FIGURE l5) opposed to the conicalsurface N of the piston 98 for decelerating the two pistons at theconclusion of their hig. speed stroke by forcing the water out frombetween these two surfaces as the shuttle NGE nears the end of itsStroke.

The static seal is of tough resilient material similar to the seals inrepeaters 7), 70 and 70A, and the seal 163 may be made of this material;however, if desired, the seal 102 which defines the discharge port fromthe charge chamber 113 may be made from a very tough and durablellame-resistant material such as strong metal, eg., staifiless steel,beryllium, bronze and the like. In the repeaters into which fuel isinjected and burned, it is advantageous to form this seal 102 of a verytough and hard strong material such as metal to withstand the dischargeof heated combustion products therethrough. A resilient sealing element155, for example such as an O- ring provides a seal with the casing, andthe seal permits the metal seal 102 to rise slightly away from ashoulder 147 when it is in sealing engagement with the piston 98 so thatthe lip 114 of the other pis-ton presses firmly against the static seal115. Spring means 159, for example such as a wave spring urges themovable seal element 162 down toward the shoulder 147.

ln this illustrative example the chamber 113 has a volume of ten cubicinches, the diameter of the piston is 1.75 inches, and the accelerationdistance E is 3%; of an inch. The shuttle 100B attains a velocity inexcess of 40 feet per second before releaing the pressure luil, and thehigh-pressure gas is discharged from this repeater 76B in the order of afew miliseconds after the piston 98 has left the end 132 of the cylinder95.

The lower end of the cylinder 97 is closed by an end wall 156 whichcontains the till passage 90. A flange 157 on the container 94 isextended and contains an additional row of bolt holes 153 for mountingpurposes, if desired.

The repeater 70B shown in FIGURE 15A is similar to the repeater 70B ofFIGURE 15, except that the perimeter of the piston 99 is circular, andthe by-pass passages 127 are provided by grooves in the cylinder wall97. The pressure iiuid rushes up through these grooves 127' as shown bythe ow arrow thus tending to equalize the pressure acting upon oppositesides of the operating piston 99', and the shuttle 153B accelerates veryrapidly toward the open position, while the lands 123 between thegrooves 127 serve to guide the piston.

As shown in FIGURES 9 and 10 the acoustical impulse generator repeaterapparatus may conveniently be mounted on a submersible housing andchassis unit 160 having a hollow tail boom 161 and tail tins 162 forstabilizing the unit as it is towed through the water. A towing arm 1&3is pivotally attached at 154 to a top adjustable mounting bracket 165having a plurality of pivot holes 16d therein. A towing cable 167extendidg from the ship 20 is attached to the upper end of the arm 163.A pair of protective guards 168 straddle the arm 163 to protect the hose83 and the electric control cable 57 from accidentally being pinched orsheared between the arm 163 and the housing 17% in the event the unit166 is placed upside down on the deck of the ship.

Any of the acoustical repeaters and any of lthe exporation systemsdiscussed above and those discussed hereinafter may use such a unit 159if desired.

A seen most clearly in FIGURE l0, a removable section 171 of the housingsurrounds the repeater apparatus and is secured by bolts 172 to a heavymounting plate 173. The space 174 within the housing 170 above themounting plate 173 is a water-tight chamber as explained in detailfurther below, but water is free -to enter the remaining spaces withinthe unit 160 for pressure equalization. The water may enter a lowerspace 175 through a large opening 176 surrounding the repeater apparatusand ow into a forward space 177 in front of a partition 178 and enter arear space 179 communicating with the interior of the tail boom 161which is also open at its tail end. The front partition 178 and a rearpartition 180 close off the water-tight compartment 174, which remainslled with a suitable insulating fluid, for example such as air, oil, orthe like, during operation so as to protect the various cornponents andcontrol elements of the systems housed therein as shown.

The electric cable 57 enters the housing through a rubber grommet 181(FIGURE 9) and then passes through a water-tight seal 182 in thepartiion 180 and extends to a terminal panel `block 184 within thecompartment 174 to which one or more of the various solenoid valves 61,62 and 63 are connected by suitable leads as shown, depending upon whichof the control systems is used as shown in FIGURES 2, 3, 4, 11, 14 or17. The hose S3 enters through another gromme-t 185 and is connectedthrough a fitting 186 and through a removable base plate 187 to thelines to the respective controllable valve means, as shown in thesystems of FIGURES 2, 3, 4, 1l, 14 or 17. The base plate 187 isremovably fastened by studs 133, and an O-ring gasket 139 provides aseal.

A pressure relief valve 190 (FIGURE 9) prevents the pressure in thecompartment 174 from rising excessively in the event of bleeding orslight leakage of high pressure gas into this compartment. For strengthand rigidity, the tiring passage 92 extends directly from the firingvalve through the base plate 187 and suitable O-ring gaskets 191 providesealing means.

In FIGS. 1l and 12 the principles of the invention are shown as appliedto a pneumatic acoustical device comprising a cylinder 220 having endwalls 221 and 222. Ports 223 and 224 are provided within the end walls221 and 222 and they are in axial aligned relation. The port 223 is ofsomewhat smaller diameter than that of port 224 for a purpose to bedescribed later. A piston rod 225 may extend through the cylinder 220,and it may support pistons 226 and 227 spaced therealong so that lin oneaxial position of rod 225, pistons 226 and 227 close ports 223 and 224,and in another position open said ports. The piston 226 may be threadedonto the end of the rod 225, while the piston 227 may be rigidly heldagainst a collar 22S on rod 225 by a nut means 229 threaded onto rod225.

The end wall 222 may include an internally threaded flange 230 forAreceiving a hollow cap member 231 that forms a chamber 232 having itsone side closed by piston 227 when the latter is in its uppermostposition. The wall of the cap 231 may overlie the piston 227 thereby tolimit its movement in one direction.

The piston rods 225 may extend upwardly above the end cap 231 and mayhave an adjustable stop 233 held thereto by a jam nut 234. A spring 235within cylinder 220 may act against one surface of piston 227 and a disk236, which latter may adjustably be xed at a predetermined locationwithin the cylinder 226 by means (not shown) fixing it to the side wallthereof. The disk 236 may be provided with large passages 237therethrough so as not to interfere with the free flow of fluid from oneto 1d the other side thereof. The piston rod 225, of course, makes asliding t with a bored boss 233 of the disk 236i. From the foregoing itis evident that spring 235 normally assists in the return of the pistonrods 225 and pistons 226 and 227 to the position shown in FIG. l1.

The cylinders 22) may be c-onnected by a line 239 to a solenoid operatedvalve 240. The chamber 232 may also be connected through a line 241 tothe valve 240, and the valve 249 may be connected to a high-pressurecompressor 242 through a tiexible line 243.

With the apparatus in the condition shown in FIG. 1l, with chamber 232vented through the valve 240 and line 243 connected to line 239 throughvalve 240, fluid under a great pressure may be supplied to the cylinder229. Since piston 227 is of greater area than that of piston 226, theapparatus remains in the condition shown in FIG. 1l.

Upon operating the solenoid valve to connect chamber 232 with cylinder22d, the pressure on each side of piston 227 is equalized, causing thepiston 226 and rod 225 to move downwardly very rapidly, permitting thevery rapid escape of the pressure uid in cylinder 220 through port 223,which action produces an acoustical wave of great intensity. Operatingvalve 240 to vent chamber 232 causes spring 235 to return the rod 225and pis tons 226, 227 to the position shown in FIG. 1l, and reconnectingline 243 to line 239 through valve 24) recharges cylinder 220preparatory to producing another acoustical wave.

Referring to FIG. 13, the principles of the invention are shown asapplied to an apparatus similar to that shown in FIG. 1l. The cylinder22) is supported on legs 262,

and a cylinder 263 extends downwardly from port 223, within which thepiston 226 reciprocates. The piston rod 225 extends downwardly throughthe cylinder 263 and supports at its lower end a hammer 264. The lowerend of the cylinder 263 may be provided with a counterbore 265 whichvents the high pressure lluid from cylinder 263 when piston 226 reachesthe bore 265. From the foregoing it is evident that upon tripping thesolenoid valve 240 (FIG. 1l), the full pressure of the fluid withincylinder 220 acts on the piston 226, imparting a very great accelerationto the hammer 264.

The embodiment shown in FIG. 14 is similar to the apparatus shown inFIG. 11, except it includes a device 266 for injecting fuel under highpressure into the cylinder 226 when the latter is under pressure fromsource line 243. An electrical heating element 267 may be mounted incylinder 226 for the purpose of igniing the fuel as it is injected intocylinder 229. The embodiment shown in FIG. 14 is triggered by theinjection of the fuel into cylinder 221i, and a slight interval later,the solenoid 240 may be actuated, causing the downward thrust of pistons226 and 227 when the highly pressurized fluid exhausts from port 223,producing the acoustical wave of great intensity. It is to be understoodthat the fuel injection means 266 of the embodiment shown in FIG. I4may, if desired, be incorporated with any of the other embodiments ofthe invention with equal facility.

The embodiment of FIGURE 17 is similar to the apparatus shown in FIGURES4, l5 and 16, except that it includes a device 266, for example such asan oil burner spray nozzle, a fuel injector of the type for a dieselengine, and the like for injecting fuel under high pressure into thecharge-receiving chamber 113 after it has been filled with air underhigh pressure. An electrical heating element 267, for example aresistance wire element, serves to ignite the fuel, thus greatly raisingthe pressure in the chamber 113. After the fuel has burned, the ringcontrol means 61 is actuated by an electrical signal for abruptlyreleasing the products of combustion so as to produce an intenseacoustical impulse. The fuel injection device 266 is mounted at an anglewith respect to a radial line of the cylinder 113 so as to produce aswirling motion of the charge within the chamber 113. It will beunderstood that fuel injection devices as shown in FIGURES 14, 17 andsavants 17A may be incorporated with any of the embodiments of theinvention disclosed herein.

The embodiment IGI shown in FIGURE 17A is similar to the apparatus shownin FIGURES 4, 15, 16 and 17, except that the device 266 for injectingfuel and the igniting means 267 are arranged so as to burn the fuel inthe chamber mi... The increase in gas pressure in the chamber 145-3causes gas to flow up through the passage 153, thus also raising thepressure in the chamber 113. The apparatus is fired by admitting gasthrough the firing passage 92.

In FIGURE 2O is shown an embodiment of the invention similar to that ofFIGURE 18, except that the shuttle 10? includes a small orifice 27d forproviding communication through the wall of the hollow piston rod lulbetween the return chamber t/i and the charge-containing chamber 113.This orifice 278 may be provided in any of the embodiments of FIGURES 2,3, 5, 5A, and 18. By providing this passage 276, the chamber 113 isfilled by fluid supplied through the return line (FIGURES 2, 3, 5 and18); so that the return means serves to fill the repeater after theshuttle 199 has been returned to its initial position. Thus, the fillvalve 63, till line 89, and fill port 90 can be omitted, enabling theuse of a control system of the type shown in FIGURE 4, wherein a firingvalve 61 provides the control action.

The amplitude (source level) of the repeater acoustical pulse may bevaried in each of the embodiments disclosed herein by adjusting thepressure in or the volume of the charge-containing chamber. The pressureand volume may be adjusted independently of each other. The frequency ofthe acoustical pulse may also be controlled by adjusting the pressure inor the `volume of the charge-containing chamber.

It is to be noted that it is in advantage of the illustrativeembodiments of the present invention disclosed herein that they enablethese two characteristics of the pulse (source level and frequencycontent) to be varied independently of each other. For example, if it isdesired to vary the frequency of the pulse while maintaining the sourcelevel constant, the pressure in the charge-containing chamber may bevaried in one direction, eg., increased, while the volume is varied inthe other direction, e.g., decreased.

Increasing the volume of the charge-containing chamber lowers thefrequency and increases the intensity for a given pressure providingthat the apparatus releases the high-pressure iluid within the samebrief instant.

The embodiments of FIGURES 18 and 19 are provided with means 279 foradjusting the effective volume of the charge-containing chamber. Theposition of a piston 2gb is moved along a volume adjusting cylinder 281during operation by adjusting the position of a control piston 282 in acontrol cylinder 283 on the ship. Suitable liquid such as hydraulicfluid 2Stills the region 28S behind the controlled piston 28o and theregion 236 in front of the piston 232. A crank 287 and feed-screw 2&8adjust the position of the piston 28u by displacing the hydraulic liquid234 by moving the piston 282 against the action of a spring in thechamber 286.

It is to be understood that the volume-adjusting means 279 of theembodiments of FIGURES 18 and 19, may if desired be incorporated withany of the other embodiments of the invention including those whichutilize fuel injection.

In the foregoing illustrative examples of the present invention thecontrol signal for initiating the firing of the repeater has been anelectrical signal for actuating a solenoid valve. As furtherillustrative embodiments of the methods and apparatus of the inventionit is noted that these valves can be replaced by fluid-actuated valvessuch as pneumatically operated valves, valves operated by hydraulic uid,and the like. In these fluid-actuated control systems the control signalis transmitted through a Huid I d containing line such as a hydraulicline, pneumatic line, and the like for tiring the repeater.

Also, with reference to the embodiment of FIGURE 17 wherein the shuttleis returned and held by a combined return and operating chamber 148 (seeFIGURE 15), and the fuel is injected into the charge-containing chamber113, it is noted that a sudden rise in pressure in the charge chamber113 relative to chamber 143 can be used to fire the repeater. Therestriction 15d causes a delay in the rise in pressure in the operatingchamber 148 when the pressure is suddenly raised in the chamber 113.Thus, a substantial pressure differential may be created for a briefperiod when intense combustion occurs in the charge chamber 113.Consequently, the shuttle-holding force being exerted by the operatingpiston 99 is over-balanced by the higher pressure arising in the chargechamber 113, resulting from the sudden injection and burning ofsubstantial quantities of fuel. It is noted that the embodiment ofFIGURE 17 can be fired by the sudden injection and burning of fuel inresponse to a suitable signal. This signal may be transmitted by varioustransmission means such as an electrical signal, a hydraulic signal,pneumatic signal, and the like. Alternatively, the fuel may be injectedand then ignited sometime after injection by an ignition signal.

Instead of suddenly raising the pressure in the chamber 113, adifferential between the pressures in the two chambers 1.13 and 148 canalso be created by suddenly dropping the pressure in the chamber 148,for example by discharging iuid abruptly from the line 86 by opening apressurerelease valve in this line.

In systems where it is desired to produce a sudden and substantialamount of combustion in the repeater of FIG- URE 17, and yet it isdesired to initiate tiring by admitting fluid through the firing line 92(FIGURE 15) in response to a firing signal, then the area L of theoperating piston 99 is increased relative to the area K of the openingand closing piston 98. The ratio of areas is determined by the maximumdifferential in pressure which is desired to be retained, that is, theproduct of the effective area L times the pressure in chamber 148 mustat all times exceed the product of the effective area K times thepressure in chamber 113. Then the shuttle is retained in place, and itsviolent acceleration is initiated by admitting uid through the firingpassage 92 in response to a tiring signal.

The piston ring 149 also provides the function of preventing accidentaltiring, the same as is done by the bleed hole 144 (FIGURE 5). Any slightleakage tending to raise the pressure against the piston surface M isoffset by leal:- ing past the piston ring 149 and then-ce out to theexterior of the apparatus through the vent means 96. The lower surfaceof the annular guide member 152 may include a plurality of shallowradial grooves communicating with the region surrounding the piston rod161 for assuring the escape of any undesired iuid from behind the piston98 until the desired instant of tiring has arrived.

The embodiments of FIGURES 4, 15, 15A, 17, 18, 19 and 2O are adapted tobe arranged for self-actuating-ring operation, i.e. automatic operation,which is an advantage in enabling the control of the repeater to beaccomplished by means ofthe characteristics of the pressure in thesupply line S3, as may be desired in certain systems. In order toprovide for self-actuating, ring operation, automatic operation, theeffective area of the surface K is made larger than the effective areaof the surface L. This is accomplished in either of two ways: (l) byactually making the effective area K of piston 9S larger than theeffective area L of pison 99, or (2) the effective area of the sealingelement 102 is added to the area of the piston 98 so that their combinedeffective area is greater than the effective area L of the piston 919.This second condition (2) immediately above is obtained by having theshuttle sufficiently long relative to the axial distance between theshoulder 147 and the lower surface of the housing member 152 so that theannular seal 102 becomes raised away from contact with the shoulder 147when the surface M of the piston 99 abuts against the housing member152.

